When the Implant Needs to Last a Lifetime, New Fastener Thread Form Technology is Key

         With the lives of patients as well as the reputations of surgeons and medical device companies at stake, medical implants face some of the most rigorous performace requirements of any industry. Yet despite all the recent technology applied to implants, they still require simple fasteners to function properly. Once inside the body, these fasteners often must endure severe loading and shock for millions of cycles throughout the patient's lifetime.
         Because these fasteners are so critical, medical device manufacturers have been taking advantage of the unique Spiralock thread design that not only combats vibration and shock but also safeguards product quality and performance whether the implant is permanent or temporary.
         When Biomet, Inc. developed a new artificial knee implant, its innovative development was highly dependent on the threaded fastener that had to guarantee repetitive loading without loosening. Knee implant surgery is designed to be permanent, so the implant assembly must function for the rest of the patient's life, without failure. Re-tightening the implant in a second or third operation is not an option. Conventional fastening methods such as add-on locking components, adhesives, patches, and inserts will be rejected by the body, and aren't acceptable methods for implant use.
         Biomet's final choice came down to a snap-fit type locking fastener and the Spiralock thread form. Extensive fatigue tests showed that the snap-fit fasteners tended to work loose under extensive loading, while Spiralock did not fail, regardless of the length and severity of the tests. After several years of in body application, not a single screw fastened with the Spiralock thread form has come loose.

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